Loud speaker apparatus and methods



June 21, 1932. lc@- A, FESSENDEN 1,863,840

LOUD SPEAKER APPARATUS AND METHOD Original Filed May 2l, 1924 l \P/A/va sau/vows 50420 Patented June 21, 1932 UNITED STATES PATENT OFFICE REGINALD A. FESSENDEN, OF CHESTNUT HILL, MASSACHUSETTS, ASSIGNOR TO SUB- MARINE SIGNAL COMPANY, OF PORTLAND, MAINE, A CORPORATION 0F MAINE LOUD SPEAKER APPARATUS AND METHODS Original application led May 21, 1924, Serial No. 714,899. Patent No. 1,854,025, dated April 12, 1932.

I Divided and this application filed January 6, 1927. Serial No. 159,366.

disturbing electrical impulses, and has for its4 object increased eficiency in said reproduction and the elimination of said static and other disturbing electrical impulses.

Figures 1, 2 and 3, accompanying this specification, illustrate, partly diagrammatically, apparatus suitable for carrying out my invention.

Consequent on the extended use of the wireless telephone and broadcasting, four serious defects imposed attention:

(a) Great variation in intensity of reproduction with distance from the reproducer; the intensity falling oit as the square of the distance. 1

Inability of the standard loud-speakers to reproduce the lower tones of the human voice and of music.

(c) Great variation in eliiciency of reproduction of diderent tones, ratios of ten to one, orl more, being common.

(d) Inability to keep out abrupt electrical extraneous disturbances, i. e. electrical impulses which were abrupt and which it was not desired to transmit, such as static.

The first of these defects was overcome by the invention of the sound area source, (U. S. Patent 1,213,176, June 27th, 1916), by means of which it became possible to make the intensity of reproduction substantially the same at the far end of a large hall as close up to the reproducer.

The second was overcome by the discovery and invention, as the result of considerable mathematical and experimental work, and

contrary to all previous theory, that, to obtain eicient reproduction the diameter of the sound source must have a certain definite ratio to the wave length of the sounds which it was desired to reproduce eiciently. Consequently, that it was only necessary to decide what were the lowest tones which it was desired to hear, and then to make thc diameter of the sound source have the required fraction of that wave length. (U. S. Patents 1,207,388, Jan. 29th, 1913, and 1,277 562, Feb. 28th, 1917), which for ordinary speech is seven and a haltI inches or more (Spec. of 1,277,- 562, p. 1, l. 67.). The former standard loud speakers with diaphragms of 11/2 to 2 inches diameter have therefore, within a few years of the appreciationof this discovery, been entirely supplanted by diaphragms of 10 inches or more di ameter. v

T'he third was overcome by the discovery and invention of loud speakers having substantially a flat eiiciency characteristic from the lowest audible to the highest audible tones; and which loud speakers are in part disclosed and claimed in the patent application Serial N0. 714,899, tiled May 21, 1924, matured as Patent No. 1,854,025, April12, 1932, of which this is a division.

The fourth defect may be substantially eliminated by the method disclosed in the Vpresent application. It was discovered that if a plurality of resonant elements of suitable masses and suitably elastic and suitably damped and suitably chosen, were attached to an area source; for example strings strung across the face of a large diaphragm, that by proper ,proportioning diaphragmA and resonant elements, the area source, if driven in any suitable manner, for example, by the electro-magnetic loud speaker mechanism shown in Fig. 2, or the magneto-striction loud speaker mechanism shownin Fig. 1, or in similar manner, e. g. as shown in a pplicants area-source'Patents 1,213,176 and 1,277,562, above referred to, the reproduction was substantially perfect.

It was alsov discovered that sources of this type have the further advantage that disturbing noises could be entirely cut out. Even when a violin, which has only four strings, was used as loud speaker, for an electro-phonograph, a'substantially large amount of the scratching from the phonograph disc was eliminated, and by adding additional was used for receiving radio broadcasting, it

has a sufficient number of resonant elements vui attached to its sounding board, i. e., the piano strings, and sufficient area to act extremely efiiciently as a static eliminator in addition to its other properties of giving absolutely faithful reproduction of all sounds from the lowest to the highest, and of giving equal intensity of sound in all parts of the room. As an illustration of the eiiciency of the piano as a static eliminator, for the past three summers, applicant wh'o uses one and the members of his householdV and guests have never heard `static or known that there was anyk The sounding board forms the area'source and may be driven in any suit-able manner, e. g., vby the electromagnetic loud speaker mechamsm shown in Figure 2, or the'magneto-'striction loud speaker mechanism shown in Figure 1, or in similar manner, for example, as shown in applicants area-source loud speaker Patents 1,213,176 and 1,277,562, above referred to. Or by a magneto-striction loud speaker mechanism like that shown inA Figure 1, but comprising instead of a single wire f 43, a large numberof thinY wires each at tached to different terminals, but all actuated simultaneously byone coil, and this device made resonant by well known means so as to respond overa range of a la'rge number of frequencies. Or by any of the mechanisms well known in the art, such as that ldescribed as attached to the back of the sounding board of the piano in applicants article in the Boston American Aug. 28th, 1924.

The Ydriving mechanism may be attached to any suitable part of the sounding board of the piano in any suitable manner, for eX- ample, by cement, but as the'metliodof attachment and the method of driving are not claimed herein, further particulars will not be necessary as suitable means are well known in the art.

Figure 1 shows the attachment of the well known magneto-striction driving apparatus to a piano sounding board, and 43 a nickel or eok iron wire attached to timing. pins 41, 42, fastenedto the piano sounding board 11, and

44 is the magnetizing coil leading through the battery cell 45 to the terminals of the secondary of the receiving set or telephone line. Figure 2 shows another well known'type of loud speaker electromechanism where the -wires 59, 59 are preferably of soft iron or nickel and are screwed into the circular spring 60 of magnetic material so as to leave a small air gap between them, as shown. 22, 23 are a magnetizing coil and a source of current, and 61 is a coil connected as shown tol leads 63 going to the transmitter or receiver. 62 is a small ball used as an inertia to oppose the pull on the wire when the two wires 59, 59 are retracted together by the action of the currents flowing in the coil 61, as shown. Or, when desired, in place of using the small ball on the'wire, the Wire may, as is customary with this type of telephone mechanism,be fastened to a post or other support.

Whichy particular method of drive is used will depend upon circumstances. In the arrangement shown in Figure 1, the change in length of the wire 43 caused by the magnetostrictiveeffect of the received telephonie currents flowinor through the coil 44 bends the entire sounding board in and out thereby causing the whole sounding board to act as a unitary large diaphragm. Also byemploying a number of such wires 43 and suitably arranging them as shown in the parent application, the piano loud speaker can he made so as to have no detrimental selective resonance.

What I claim is: f

1. In the art of reproducing electrically transmitted sounds, the method of eliminating the effect of static and other disturbing electrical impulses by causing the transmitted impulses, both sound producing andV disturbing, to -act-uate the sounding board of a piano as a loud speaker; whereby the disturbing impulses are reproduced with much less relative intensity than the soundfproducing impulses.

2. In the art of reproducing sounds transmittedelectrically, the method of eliminating the eli'ects of static and other disturbing electrical impulses which comprises actuating, by the received impulses, the sounding board of a piano as a loud speaker. i e

3. In the art of reproducing sounds trans'- mitted electrically, the method of reducing the ratio of the effects of static and other dis-Y turbing impulses to those yfor producing the sounds which it is desired to reproduce; comprising actuating bythe received impulses, a loud speaker electromechanism attached to the sound board of a piano.

4. The method of reproducing electrically transmitted sounds which consists in vibrating by the electrically transmitted impulses the sound board of a piano and transmitting said vibrations from said piano sound board to the air, whereby a loud speaker actionof said piano sound board is produced.

5. The method of reproducing electrically transmitted sounds which consists in electromagnetically producing vibrations in a piano sound board responsive to the transmitted electrical impulses, and transmitting said vib rations from the piano sound board to the air.

6. A loud speaker comprising a piano sound board and electromagnetic means responsive to the transmitted electrical current impulses for actuating by direct operative Contact said sound board.

7. A loud speaker comprising a piano sound board and loud speaker electrical mechanism in operative contact with said sound board for actuating the same.

8. A loud speaker comprising a piano sound board and loud speaker electrical mechanism attached to said sound board for actuating the same.

9. A loud speaker' comprising a loud speaker electrical mechanism and a piano sound board, said loud speaker electrical mechanism actuating said piano sound board by (llirect mechanical operative Contact there- Wit 10. An electrically operated loud-speaker unit comprising a vibratable element, and means for attaching the vibratable element of said loud-speaker unit directly to the sounding board of a piano.

11. A piano comprising a sounding board and strings attached to one side of said board capable of producing a plurality of chromatic scales, an electrically operated loud-speaker unit having a vibratable element, and means for connecting said vibratable element direct- 1y to said sounding board to effect vibration of the board, the' vibration of said board setting said strings into vibration.

12. A piano comprising a sounding board and strings attached to said sounding board capable of producing a plurality of chromatic scales, a loud-speaker unit comprising a vibratable element mounted at one side of the board and arranged so that the impulses of said vibratable element will be directly transmitted to said sounding board .to set the sounding board into vibration, the said vibration of said board setting the strings into Vibration.

13. A piano comprising a sounding board and a plurality of strings vibratable at their natural frequencies ovei` substantially the entire range of audible sounds, and a loudspeaker vibrator mechanism connected to said sounding board and ,adapted to vibrate said sounding board and strings over substantially all of said audible range.

14. An area source of sound and a plurality of resonant elements connected thereto, resonant at their natural frequencies over substantially the range of response desired, and a. vibratable mechanism connected to said sounding board and adapted to vibrate said sounding board over substantially all of the desired range, and thereby to set in vibration the said resonant elements.

15. A sound producing device comprising an area source, a plurality of magnetostric- REGINALD A. FE SENDEN. 

